[Boost-users] Smart pointers and STL allocators

From: Mark A. Gibbs (gibbsmark_at_[hidden])
Date: 2003-11-16 12:54:16

I have a couple of questions about combining smart pointers and STL 
allocators.

First of all, am I right in assuming that I can use the shared_* 
templates right out of the box, as long as I define a custom deleter 
that uses the allocator's deallocate function?

But if that's so, how exactly is it done? Part of my confusion comes 
from the fact that the STL allocator documentation I've come across 
isn't exactly clear on the semantics of allocators (I don't have a copy 
of the standard). For instance, I'm not 100% sure whether or not I have 
to call construct() after allocate() and destroy() before deallocate(). 
This is what I have so far:

class allocator_helper
{
public:
    allocator_helper(allocator_type& a) : a_(a)
    {}

    void operator()(void const* p) const
    {
       a_.deallocate(static_cast<allocator_type::pointer>(p));
    }

private:
    allocator_type& a_;
};

foo* bar = static_cast<foo*>(get_allocator().allocate(1));
shared_ptr<foo> p_foo(bar, allocator_helper(get_allocator()));

foo* baz = static_cast<foo*>(get_allocator().allocate(10));
shared_array<foo> p_foo(baz, allocator_helper(get_allocator()));

Now, for scoped_* I would probably have to rewrite them to use the 
allocator, right? Or is there a way to use allocators with the existing 
scoped_* templates?

Mark